Mammalian proviruses are highly virulent in newborn mice, causing damage to several organs, including the central nervous system (CNS) and heart. In these organs, reovirus disease is dependent on the intrinsic cellular responses elicited upon infection. Reovirus encephalitis and myocarditis are both associated with apoptosis, and targeted ablation of either cellular apoptotic pathways or reovirus determinants of apoptosis induction attenuates reovirus disease. Similarly, pathogenesis is also influenced by the host interferon (IFN) response; both the levels of type I IFNs induced by reovirus infection, and the sensitivity of reovirus strains to IFN, correlate with disease severity. Both IFN induction and apoptosis following reovirus infection are linked to innate immune responses dependent on transcription factor IRF-3. The primary goal of the proposed research is to elucidate the regulatory mechanisms underlying host cell innate immune responses to reovirus infection that mediate apoptosis, IFN induction, and reovirus restriction. Three integrated specific aims are proposed to define these mechanisms. In Specific Aim 1, mechanisms that regulate the induction of host cell pro-apoptotic factors via IRF-3 will be identified. We will examine the role of transcriptional co-activators and chromatin structure on IRF-3 promoter occupancy and activity. In Specific Aim 2, mechanisms of IFN-mediated restriction of reovirus infection will be characterized. Specific Aim 3 will facilitate the other two aims and enhance the undergraduate research program at Colgate University by supporting a laboratory component for an elective Virology course, which will engage students in a semester- long project to generate and characterize reovirus reassortants, and a senior-level research course in which students conduct the independent research projects outlined in Specific Aims 1 and 2. Broadly, this research will enhance understanding of the mechanisms regulating a key cell fate decision: whether to commit to an antiviral response, via IFN and ISG synthesis, or whether, and when, to initiate programmed cell death mechanisms. This research also will provide insight into mechanisms through which type I IFNs restrict reovirus infection. As other pathogenic microbes elicit similar cellular responses, this research program will uncover conserved mechanisms of infectious disease pathogenesis.